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Introduction
The Hashtable class in Java is a part of the java.util package.
It is a legacy class that implements a hash table, which maps keys to values.
It is synchronized and can be used in multithreaded environments.
Table of Contents
- What is the
HashtableClass? - Common Methods
- Examples of Using the
HashtableClass - Conclusion
1. What is the Hashtable Class?
The Hashtable class implements a hash table data structure, which allows you to store and retrieve key-value pairs. It is synchronized, meaning it is thread-safe and can be shared among multiple threads without additional synchronization.
2. Common Methods
put(K key, V value): Maps the specified key to the specified value.get(Object key): Returns the value to which the specified key is mapped.remove(Object key): Removes the key (and its corresponding value) from the hashtable.containsKey(Object key): Returnstrueif the hashtable contains the specified key.containsValue(Object value): Returnstrueif the hashtable maps one or more keys to the specified value.size(): Returns the number of key-value mappings in the hashtable.isEmpty(): Returnstrueif the hashtable contains no key-value mappings.keys(): Returns an enumeration of the keys in the hashtable.elements(): Returns an enumeration of the values in the hashtable.clear(): Clears the hashtable so that it contains no key-value mappings.
3. Examples of Using the Hashtable Class
Example 1: Creating and Using a Hashtable
This example demonstrates how to create and use a Hashtable with key-value pairs.
import java.util.Hashtable;
public class HashtableExample {
public static void main(String[] args) {
Hashtable<String, Integer> hashtable = new Hashtable<>();
// Adding elements
hashtable.put("Apple", 1);
hashtable.put("Banana", 2);
hashtable.put("Cherry", 3);
// Retrieving elements
System.out.println("Value for 'Apple': " + hashtable.get("Apple"));
// Checking if key exists
System.out.println("Contains key 'Banana': " + hashtable.containsKey("Banana"));
// Checking if value exists
System.out.println("Contains value 3: " + hashtable.containsValue(3));
// Removing an element
hashtable.remove("Banana");
System.out.println("After removing 'Banana': " + hashtable);
// Getting the size of the hashtable
System.out.println("Size of hashtable: " + hashtable.size());
}
}
Output:
Value for 'Apple': 1
Contains key 'Banana': true
Contains value 3: true
After removing 'Banana': {Cherry=3, Apple=1}
Size of hashtable: 2
Example 2: Iterating Over Keys and Values
This example shows how to iterate over the keys and values in a Hashtable.
import java.util.Enumeration;
import java.util.Hashtable;
public class HashtableIterationExample {
public static void main(String[] args) {
Hashtable<String, Integer> hashtable = new Hashtable<>();
hashtable.put("Apple", 1);
hashtable.put("Banana", 2);
hashtable.put("Cherry", 3);
// Iterating over keys
Enumeration<String> keys = hashtable.keys();
System.out.println("Keys:");
while (keys.hasMoreElements()) {
System.out.println(keys.nextElement());
}
// Iterating over values
Enumeration<Integer> values = hashtable.elements();
System.out.println("Values:");
while (values.hasMoreElements()) {
System.out.println(values.nextElement());
}
}
}
Output:
Keys:
Cherry
Apple
Banana
Values:
3
1
2
Example 3: Clearing the Hashtable
This example demonstrates how to clear all key-value mappings from a Hashtable.
import java.util.Hashtable;
public class HashtableClearExample {
public static void main(String[] args) {
Hashtable<String, Integer> hashtable = new Hashtable<>();
hashtable.put("Apple", 1);
hashtable.put("Banana", 2);
hashtable.put("Cherry", 3);
System.out.println("Hashtable before clear: " + hashtable);
// Clearing the hashtable
hashtable.clear();
System.out.println("Hashtable after clear: " + hashtable);
System.out.println("Is hashtable empty? " + hashtable.isEmpty());
}
}
Output:
Hashtable before clear: {Cherry=3, Apple=1, Banana=2}
Hashtable after clear: {}
Is hashtable empty? true
4. Conclusion
The Hashtable class in Java provides a synchronized key-value mapping, making it suitable for use in multithreaded environments. Although it has largely been replaced by the HashMap class due to its better performance in non-synchronized contexts, Hashtable is still useful when thread safety is required without additional synchronization. The examples provided demonstrate common usage patterns and highlight the capabilities of the Hashtable class.
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